Demographics of the dataset at entry to each cohort
| Age (years) | NSAP | Percentage of female patients | Control cohort | Control:case ratios |
|---|---|---|---|---|
| 0–2 | 5139 | 43.6 | 300 787 | 58.5 |
| 3–5 | 20 974 | 42.3 | 428 021 | 20.4 |
| 6–12 | 138 267 | 49.0 | 632 553 | 4.6 |
| 13–16 | 104 243 | 68.1 | 323 562 | 3.1 |
| All | 268 623 | 55.8 | 1 684 923 | 6.3 |
The diagnoses used to create the control cohort were squint, otitis media, otitis externa, upper respiratory tract infections, nasal polyp, deflected septum, impacted tooth and other selected disorders of teeth, inguinal hernia, nail diseases, sebaceous cyst, selected limb fractures, dislocations sprains and strains, superficial injury and contusion, tonsillectomy and adenoidectomy. All calculations of observed and expected numbers of each outcome condition were undertaken within age strata (eg, in the 0–2 group, 5139 NSAP cases were compared with 300 787 controls) before being summed as stratum-standardised results (see Method section). All eligible control patients were included in the calculations (nothing is gained by discarding controls to get equal ratios of controls to cases in each stratum).
NSAP. non-specific abdominal pain.